The present invention relates to a fluid bearing equipment for use in an office automation system and an audiovisual system.
Fluid bearing equipments are generally used in rotary head cylinders for tabletop VTRs and camera-incorporated VTRs, in polygon scanner motors for laser copiers, and in recording medium rotation drivers for floppy disk devices and hard disk devices.
Specifically, the hard disk devices have higher memory capacities and higher data transfer speeds. This requires a disk rotating device for use in a recording apparatus of this type to be capable of high-speed and high-precision rotation.
To this end, a fluid bearing equipment as disclosed in U.S. Pat. No. 5,504,637 is used for a rotary main shaft of the recording apparatus.
The fluid bearing equipment has a construction as shown in FIGS. 6 and 7.
The fluid bearing equipment includes a stationary shaft 1 and a rotary sleeve 2 supported around the stationary shaft 1. The stationary shaft 1 has a proximal end fixed to a lower casing 3. Hard disks 4 are fitted around the rotary sleeve 2.
Dynamic pressure generating grooves 6 are provided in an outer circumferential portion of the stationary shaft 1 in a radial-side dynamic pressure generating portion 5 defined between the stationary shaft 1 and the rotary sleeve 2.
A stationary thrust plate 9 is attached to a distal end of the stationary shaft 1 by an extension shaft 8 formed with a male thread portion 7 threaded with the stationary shaft 1.
The rotary sleeve 2 has a recessed portion 10 provided in association with the stationary thrust plate 9. An opening of the recessed portion 10 is virtually closed by a rotary thrust plate 12 which has at its center a center hole 11 of a diameter greater than the outer diameter of the extension shaft 8. The rotary thrust plate 12 is fixed to the rotary sleeve 2 by a screw 13.
In a thrust-side dynamic pressure generating portion 14 defined by the recessed portion 10 of the rotary sleeve 2, the stationary thrust plate 9 and the rotary thrust plate 12, dynamic pressure generating grooves 15, 16 are provided in upper and lower faces of the stationary thrust plate 9. The thrust-side dynamic pressure generating portion 14 and the radial-side dynamic pressure generating portion 5 are filled with a lubricating fluid.
A stator winding 17 is disposed around a proximal end portion of the stationary shaft 1 on the lower casing 3. A magnet 18 is provided on an inner circumferential surface of the rotary sleeve 2 as opposing to the stator winding 17. The extension shaft 8 is fixed to an upper casing 19 by a screw 20.
In the fluid bearing equipment having the aforesaid construction, the hard disks 4 are rotated at a high speed via the rotary sleeve 2 in a sealed space defined between the lower casing 3 and the upper casing 19 upon energization of the stator winding 17.
The rotation of the rotary sleeve 2 about the stationary shaft 1 pumps the lubricating fluid so that the rotary sleeve 2 can maintain non-contact rotation.
The dynamic pressure generating grooves 15, 16 in the thrust-side dynamic pressure generating portion 14, though no specific explanation is given thereto in U.S. Pat. 5,504,637, generally have an arrangement as disclosed in Japanese Examined Patent Publication No. 59-45844 (1984). More specifically, the dynamic pressure generating grooves are provided as herringbone grooves 22 arranged circumferentially of the stationary thrust plate 9 as shown in FIG. 8. A line 23 linking apices of the herringbone grooves is located in a radially middle position of the thrust-side dynamic pressure generating portion. The dimensions of the prior art thrust plate satisfy the equation: a=(d2xe2x88x92d1xe2x80x2) (0.5), wherein xe2x80x9cd2xe2x80x9d is the outer diameter of the plate, xe2x80x9cd1xe2x80x2xe2x80x9d is the inner diameter, and xe2x80x9caxe2x80x9d is the distance from either its outer, or inner edge to the apices of the herring bone portion.
However, the aforesaid arrangement has the following drawback.
The fluid bearing equipment of this type, which is adapted for high speed rotation and has an open portion on the upper side of the thrust-side dynamic pressure generating portion, suffers from a unique demerit such that the lubricating fluid is liable to leak out of the thrust-side dynamic pressure generating portion due to various causes such as thermal expansion of the lubricating fluid or bubbles (air) in the lubricating fluid which may occur when the temperature of the lubricating fluid rises during use or when the equipment is used in a high temperature environment, and a variation in the amount of the lubricating fluid charged into the equipment by a dispenser (i.e., an excess of the charged lubricating fluid).
It is therefore an object of the present invention to provide a fluid bearing equipment which is free from lockup or seizure of a bearing which may occur due to a deficiency of a lubricating fluid when the equipment is operated at a high rotation speed in a high temperature environment.
The fluid bearing equipment of the present invention is characterized in that a maximum pressure generating portion of a dynamic pressure generating groove provided in a thrust-side dynamic pressure generating portion is located closer to the outer circumference of a stationary thrust plate than a radially middle position of the thrust-side dynamic pressure generating portion.
With the aforesaid arrangement according to the present invention, lockup and seizure of a motor can be prevented which may otherwise occur due to a deficiency of the lubricating fluid when the equipment is operated at a high rotation speed in a high temperature environment.
In accordance with one particular embodiment of the present invention, there is provided a fluid bearing equipment which comprises a stationary shaft having at least one fixed end and a rotary sleeve supported rotatably about the stationary shaft and is adapted to pump a lubricating fluid between the stationary shaft and the rotary sleeve for non-contact rotation of the equipment, wherein the stationary shaft is provided with a stationary thrust plate, wherein the rotary sleeve has a recessed portion defined by faces thereof opposed to upper and lower faces and outer circumferential surface of the stationary thrust plate, wherein a dynamic pressure generating groove is provided in a radial-side dynamic pressure generating portion defined by an outer circumferential portion of the stationary shaft and an inner circumferential portion of a center hole formed in the rotary sleeve, wherein dynamic pressure generating grooves are provided in a thrust-side dynamic pressure generating portion defined by the stationary thrust plate, the inner circumferential surface of the recessed portion of the rotary sleeve and the faces of the rotary sleeve opposed to the stationary thrust plate, wherein the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with the lubricating fluid, wherein a maximum pressure generating portion of the dynamic pressure generating groove provided in the thrust-side dynamic pressure generating portion is located closer to the outer circumference of the stationary thrust plate than a radially middle position of the thrust-side dynamic pressure generating portion. In
In accordance with an aspect of the present invention, the fluid bearing equipment according one embodiment is characterized in that the following expression is satisfied:
d22xe2x88x92d32approximately equals d32xe2x88x92d12
wherein d1 is an effective inner diameter of a rotary-thrust-side portion of the thrust-side dynamic pressure generating portion, d2 is an outer diameter of the stationary thrust plate, and d3 is a diameter of the maximum pressure generating portion of the dynamic pressure generating groove provided in the thrust-side dynamic pressure generating portion.
In accordance with another aspect of the present invention, the fluid bearing equipment according to this same embodiment is characterized in that the dynamic pressure generating groove in the thrust-side dynamic pressure generating portion is comprised of herringbone grooves circumferentially arranged, and a line linking apices of the herringbone grooves is located closer to the outer circumference of the stationary thrust plate than the radially middle position of the thrust-side dynamic pressure generating portion.
In accordance with yet another aspect of the present invention, the fluid bearing equipment according to the previously discussed embodiment comprises: a stationary shaft having a proximal end fixed to a casing; a rotary sleeve supported rotatably about the stationary shaft and having an open portion provided adjacent one end thereof in association with a distal end of the stationary shaft, the open portion having a diameter greater than a diameter of the stationary shaft, the rotary sleeve having an outer circumference to which a load member is attached; a stationary thrust plate of a disk shape having a through-hole at its center and attached to the distal end of the stationary shaft, the stationary thrust plate having a lower face opposed to a bottom of the open portion of the rotary sleeve and an outer circumferential surface opposed to an inner circumferential surface of the open portion; an extension shaft having a proximal end threaded with the distal end of the stationary shaft thereby fixing the stationary thrust plate to the stationary shaft; and a rotary thrust plate of a disk shape fitted in the open portion of the rotary sleeve and having at its center a through-hole through which the extension shaft extends, wherein a dynamic pressure generating groove is provided in a radial-side dynamic pressure generating portion defined by an outer circumferential portion of the stationary shaft and an inner circumferential portion of a center hole formed in the rotary sleeve, wherein a dynamic pressure generating groove is provided in a thrust-side dynamic pressure generating portion defined by the stationary thrust plate, the inner circumferential surface of the open portion of the rotary sleeve and faces of the rotary sleeve opposed to the stationary thrust plate, wherein the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with a lubricating fluid, wherein the following expression is satisfied:
d2(d4xe2x88x92d2) greater than d1{(d3xe2x88x92d1)xe2x88x92(d2xe2x88x92d3)}
wherein d1 is an effective inner diameter of a rotary-thrust-side portion of the thrust-side dynamic pressure generating portion, d2 is an outer diameter of the stationary thrust plate, d3 is a diameter of a maximum pressure generating portion of the dynamic pressure generating groove provided in the thrust-side dynamic pressure generating portion and d4 is an inner diameter of the open portion of the rotary sleeve.